The present invention relates to systems, and elements, components, and compositions therefor, for monitoring and indicating the elapse of a predetermined integral of ambient conditions, such as time, temperature, humidity, actinic radiation, vaporous atmosphere, and the like, to which such a system has been exposed. Typically, for example in monitoring the useful shelf life, i.e., the span of safe or potent utility, of a product of foodstuff, medicament, or the like which is known to be affected by a thermal ambient, an indicator system, often in the form of an affixed label, is associated with the product and exhibits a readily discernible property variation, such as a change of color or color density, upon the elapse of a given time-temperature integral representing the product's shelf life. To this end, the system comprises a composition appropriately formulated to provide such a color change response substantially concurrently with elapse of the given time-temperature integral and, thus, expiration of the predesignated shelf life.
In particular, the present invention relates to responsive compositions of shelf life monitoring systems comprising substituted diacetylenic monomer components which exhibit a distinct color change as a result of and generally concomitant with a solid state polymerization effected by the ambient condition integral; typically, as in the case of a time-temperature indicator (TTI) system, the integral of time and temperature. More particularly, through novel treatment of the active substituted diacetylenic monomer component incorporated into an indicator composition, the invention provides means for readily adjusting the reactivity of the indicator composition monomer in order to simply and economically achieve a monitoring system having the desired sensitivity and responsiveness within a target integral range indicative of the prescribed shelf life parameters of an associated product.
Substituted diacetylenic monomers useful in the present invention have been studied and utilized in shelf life monitoring systems for many years. Such utility of numerous monomers comprising at least two conjugated acetylene groups (—C≡C—C≡C—) and their unique physico-chemical properties, e.g., responsiveness to persistent temperature excursions by transforming into contrastingly colored solid state polymerization reaction products, have been described, for instance, by Patel et al. (U.S. Pat. No. 3,999,946). The synthesis of these monomers and their implementation in TTI and other shelf life indicator compositions are discussed there at length and continue to be useful in formulating embodiments of the present invention. Likewise, the use of these diacetylenic monomer shelf life system components and improvements thereon, including broad ranges of substituents and complexes, and improved methods of monomer synthesis and blending in co-crystallization operations, have been described further by Patel (U.S. Pat. Nos. 4,189,399 and 4,384,980) and Preziosi et al. (U.S. Pat. Nos. 4,789,637 and 4,788,151). Such useful descriptions and examples of these diacetylenic monomer components finding application in the present invention are incorporated herein by reference.
While the consistent responses of these diacetylenic monomer components to thermal stimuli, and the monitoring system compositions upon which they rely, provide a basis for numerous highly functional and reliable TTI system products, the shear number of time-temperature integral response ranges represented in the myriad diacetylenic monomer compounds available for these uses imposes practical and economical limitations on their overall utility. Although, as noted in the referenced descriptions, each basic monomer component synthesized under given conditions with given precursors and processing materials may be relied upon to exhibit substantially consistent TTI color density profiles, and thus provide reproducible indications of shelf life end points, market-place requirements for increasing numbers of varying shelf life ranges have led to the need for complete syntheses in each instance to yield monomers of matching response profiles. Such requirements for essentially ad hoc component synthesis have been practically alleviated only by an economically perverse inventorying of an endless number of narrow response range diacetylenic monomer components. There has thus resulted a need for a ready, reliable, and cost-effective means for varying the reactivity, and thus the TTI response ranges, of a few basic such monomer components in order to enable ready and economical formulation of TTI systems which are capable of representing a wider range in the burgeoning numbers of target products for which shelf life monitoring is a marketplace necessity.
The present invention obviates the noted shortcomings and disadvantages of prior diacetylenic monomer composition TTI system products and provides such products which yield highly effective and improved ranges of reactivity and shelf life response while greatly reducing costs and achieving significant savings in system formulation time and material resources.